This is the most recent and most relevant thread regarding UI improvements. I went back 6 pages so far and nothing specific to player modifications though.

As a WoW Addon creator that still uses their account to work on their addons while not playing the game itself and it is another feature that could keep accounts active even if the game play is at a standoff, such as for those at max rank.

Obviously this isn't a priority compared to adding gameplay content but once that part of it has got itself sorted to last at least a year before a new influx of content then perhaps you could start working on enhancement options ( for want of a better phrase ) people have been asking for.